He has been prostituting himself every other day for the past three or four weeks -- the money and an opportunity of a warm bed too good to turn down.

"Some will take you home, give you clothes and anything you like," he says.

"They will treat you like their husband, their boyfriend, they will give you €200, €300, €400.

"It's very hard. How can a person be with another man like that? Those men are sick. No matter how often I do it, it doesn't get easier."

Clinging to hope

Many of the refugees cling to the promises of smugglers, who also roam the park, that with enough money they can get to western Europe illegally and declare asylum there.

"It's shocking for us, for me, for you," said Tassos.

"But for them [sex clients and smugglers] it's like new meat. With people who are desperate, it's very easy to abuse them."

Why now?

The seeming rise in unaccompanied minors prostituting themselves comes after a "one-for-one" deal brokered between the EU and Turkey in March.

The agreement stipulated that Turkey would accept back migrants who had crossed its borders into Greece, while the EU would resettle refugees directly from Turkey.

Alli has not told his mother of his plight in Greece.

But the deal effectively froze refugees in place, leaving tens of thousands stranded in Greece, a country still unable to adequately accommodate them.

Among those still waiting for shelter are around 1,200 unaccompanied minors, according to the Greek government -- but in reality the number is likely much higher.

Many refugees have not registered with authorities for fear of being sent back home after struggling to get this far as the EU has declared countries like Afghanistan "safe."

What is being done?

Greek police said in a statement that they had not had any reports of unaccompanied minors involved in the sex trade in the two specific areas we visited, but added they were aware of the problem and working to address it.

The United Nations High Commissioner for Refugees also said in a statement that authorities should make sure minors are protected.